This invention relates to an encapsulated fragrance in which the fragrance is controlled can be released by exposing the encapsulated fragrance to a solution of a predetermined pH. The invention also contemplates a process for preparing encapsulated fragrances.
There are numerous uses for a system which can release a fragrance in a controlled manner. These include the use of fragrances in substrates such as air fresheners, laundry detergents, fabric softeners, deodorants, lotions, and other household items. However, the design of a system that will release a fragrance over a period of time under repeatable predetermined conditions, has proved difficult. One problem in achieving such a design is that fragrances are generally essential oils that are composed of a plurality of compounds, each present in different quantities. Thus, it is difficult to predict how the quantity of each component of the essential oil will effect the release characteristics of the system.
U.S. Pat. No. 4,587,129 describes a method for preparing gel articles which contain up to 90% by weight of fragrance or perfume oils. The gels are prepared from a polymer having a hydroxy (lower alkoxy) 2-alkeneoate, a hydroxy (lower alkoxy) lower alkyl 2-alkeneoate, or a hydroxy poly (lower alkoxy) lower alkyl 2-alkeneoate and a polyethylenically unsaturated crosslinking agent. These materials are said to have continuous slow release properties, i.e., they release the fragrance component continuously over a long period of time. However, a drawback of the invention is that the release of the fragrance from the gels is continuous and cannot be controlled. Thus, the fragrance can be exhausted while the product in which it is contained is on the shelf, e.g., in storage, prior to use by the consumer.
A composition that functions to hold a fragrance until it is desirable to release the fragrance and then functions to release the fragrance over an extended period of time would be desirable. Thus, an object of this invention is to provide a composition which retains a fragrance until the desired time for release.
The subject invention provides compositions comprising a polymer and a fragrance, wherein said polymer comprises an acrylic acid copolymer. The acrylic acid copolymer comprises an acrylic acid monomer having the formula: 
wherein R1, R2, and R3 are independently selected from the group consisting of hydrogen and lower alkyl; and at least one ethylenically unsaturated polymerizable monomer such as acrylates, methacrylates, vinyl pyridines, vinyl ethers, acrylamides, methacrylamides, styrenes, pyrrolidones, and the like.
The fragrances useful in practicing the invention include any material which can impart a desirable odor or enhance an existing smell or odor to a substrate such as, for example air fresheners, laundry detergents, fabric softeners, deodorants, lotions, and other household items. Such fragrances generally contain at least one essential oil.
The compositions of the invention can controllably release a fragrance over an extended time period by contacting the composition with a solution having a pH which dissolves the polymer and releases the fragrance. In another embodiment, the polymer compositions of the invention may be used to form microspheres containing the fragrance.
Also contemplated is a method for preparing these compositions which comprises mixing the monomers and a fragrance and polymerizing the mixture.
The present invention provides compositions which are useful for controlled release of fragrances. The compositions of the invention can encapsulate a fragrance and controllably release the fragrance upon exposure to a solution having a predetermined pH. The compositions of the invention comprise a polymer and a fragrance. The polymers useful in practicing the invention can encapsulate the fragrance and release it at the desired time. Any fragrance which can be solubilized in the organic phase of a polymerization emulsion, and which can add a smell or odor to a substrate or is desirable to change, improve or enhance an existing smell or odor of a substrate may be incorporated in the polymers.
The polymers useful in practicing the present invention comprise
(a) an acrylic acid monomer and
(b) a second monomer having at least one polymerizable ethylenically unsaturated group, such as, for example, acrylates, methacrylates, vinyl pyridines, vinyl ethers, acrylamides, methacrylamides, pyrrolidones, styrenes, methacrylates, and the like.
The acrylic acid monomer has the formula: 
wherein R1, R2, and R3 are independently selected from the group consisting of hydrogen and lower alkyl. These polymers can be used to encapsulate the fragrance until it is desired to release it.
The lower alkyl groups include groups having from 1 to about 6 carbon atoms. Preferred groups are methyl, ethyl, isopropyl and butyl.
Typically, fragrances or perfume agents are compounds or compositions that either increase or enhance an existing smell or odor, or that impart a specific agreeable smell or odor to a substrate. These fragrances may be solids, liquids, vapors, or any combination thereof. Furthermore, they may completely or partially change state before being incorporated into a microsphere, while incorporated in a microsphere, or after being partially or completely released from a microsphere. Non-limiting examples of fragrances include essential oils, such as, for example, d-limonene, eugenol, orange, lemon, eucalyptol (cineol), clove oil and the like. Also useful in practicing the invention are commercially available fragrances which include materials, such as, for example, Autre Melange, or MixTex 1 from Givaudan-Roure, France and the like.
The amount of acrylic acid monomer in the polymer can vary from about 20% to about 80% by weight. The preferred amount of acrylic acid is from about 40% to about 60% by weight.
The release of the fragrance can be controlled by the incorporation of a pH sensitive group in the polymer composition. Examples of pH sensitive groups include carboxyl and amine groups. It is then possible to protonate the amine groups or deprotonate the carboxyl groups to dissolve the polymers and release the fragrance.
The polymers of the invention are prepared by suspension polymerization. The monomers are emulsified with water and the resulting microglobules are polymerized in situ to solid microspheres. If an organic compound, such as most perfumes and fragrances, is added to the unpolymerized mixture, it will partition into the globules. During the polymerization, the fragrance compound becomes incorporated into the polymer or polymer microspheres and protected from volatilization.
These monomers are easy to polymerize and have a strong affinity for the perfume and fragrance materials. The polymerization can be initiated by methods that are well known to those skilled in the art, such as, for example, free-radical initiators, ultraviolet light; heat and the like. Non-limiting examples of free-radical initiators include 2-2xe2x80x2,azobisisobutyronitrile (AIBN), benzoyl peroxide, cumene hydroperoxide, and the like. Suspending agents such as polyvinyl alcohol or polyvinylpyrrolidone may also be added to prevent the globules from agglomerating. If a water-soluble monomer is employed, neutral salts such as chlorides and sulfates can be added to cause phase separation.
The suspension polymerization reaction is stirred using standard equipment. The stirring rate is usually from about 200 RPM to about 800 RPM. The preferred rate is from about 250 RPM to about 400 RPM.
Polymerization can be carried out using standard additives known in the art. Examples of additives include stabilizers to reduce agglomeration; salts to reduce phase separation.
Non-limiting examples of stabilizers (suspending agents) include but are not limited to polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), polyacrylic acid (PAA), starch, gelatin, hydroxypropylmethyl cellulose phthalate (HPMCP) and the like. The stabilizing additives can be added in a range of from about 0.1 to about 5 percent and preferably at about 0.3 to about 1.0 percent.
Non-limiting examples of salts which are useful in practicing the invention are chlorides such as sodium chloride, potassium chloride, lithium chloride, calcium chloride, magnesium chloride and the like; or sulfates such as sodium sulfate, potassium can be released when contacted by a solution at the predetermined pH.
Using the conditions described herein, the polymers form hollow or solid matrix type microspheres wherein the cargo/fragrance is distributed in a carrier matrix or capsule type microspheres encapsulating liquid, vapor, or solid cargo. The amount of fragrance which may be incorporated by the microsphere is dependent on a number of factors which include the amount of material mixed with the monomer solution, as well as the affinity of the fragrance agent for the monomers. The polymer microspheres do not alter the properties of the fragrance. Any fragrance can be incorporated within the microspheres. The system is particularly advantageous for controlling the delivery of fragrance to a specific place and/or at a specific time. The targets can vary depending upon the fragrance employed.
The preferred microspheres have diameters between about 1 microns and about 500 microns, preferably between about 100 microns and about 250 microns. The microspheres can be readily blended with other solid or liquid ingredients which require a sustained release of a fragrance or a perfume agent, i.e., detergents, fabric softeners or lotions.
The size of the polymer microspheres formed by the method described herein can be controlled by manipulating a variety of physical or chemical parameters, such as the speed of the mixing during polymerization, monomer composition and the chemical structure of the fragrance.
The monomers, reagents and other additives used in practicing the present invention are commercially available from suppliers such as Aldrich Chemical Co. (Milwaukee, Wis., USA); Sigma Chemical Co. (St. Louis, Mo., USA); and Fluka Chemical Corp. (Ronkonkoma, N.Y., USA).